Let f(y)=5y110y21\displaystyle {f{{\left({y}\right)}}}={\frac{{{5}}}{{{y}-{1}}}}-{\frac{{{10}}}{{{y}^{{2}}-{1}}}}

Evaluate the limit:

limy1  f(y)=\displaystyle \lim_{{{y}\to{1}}}\ \ {f{{\left({y}\right)}}}=